Sea of blue mourns slain New York cop

Tens of thousands of officers paid tribute to one of their own at a New York funeral Saturday, as emotions ran high over recent protests against police violence, AFP reports.

But in a sign of the strain between New York's police force and its mayor, thrown into sharp relief since the officers were shot last week, numerous officers turned their backs outside as Bill de Blasio began to speak.

Vice President Joe Biden said the double murder was felt by the whole country.

"When an assassin's bullet targeted two officers, it targeted this city. And it touched the soul of the entire nation," Biden said.

"I believe that this great police force, and this incredibly diverse city can and will show the nation how to bridge any divide."

Giant screens were installed outside the church for the crowd that overflowed for blocks.

Amid the thousands of New York police, there were also officers from across the country, including from the states of California, Georgia and Indiana.

Tensions have flared in the United States in recent months over what protesters call police's racism and excessive force against blacks.

Rafael Ramos, 40, was killed alongside Wenjian Liu, 32, on December 20 following nationwide demonstrations after grand juries failed to charge white officers in the separate killings of two unarmed black men over the summer.

The shooter, 28-year-old Ismaaiyl Brinsley, who later killed himself, had posted angry, anti-government comments on Instagram that referenced the black men's deaths.

Some police and others have pushed back against protesters and claimed officials have been too sympathetic, accusing them of inciting the attack.

They called for a change in tone from officials and for demonstrators to halt protests ahead of the funerals.

Backs turned

Mayor de Blasio, in particular, has been subject to withering criticism from some of the city's 35,000 police officers for his remarks following demonstrations.

A father of biracial children, de Blasio had told reporters he counseled his teenage son Dante to take extra care when dealing with officers.

Outside the church, in a gesture seen in previous incidents since the killings, a sea of blue-uniformed police turned away in protest as de Blasio took the podium.

Current police and retired officers at the funeral warned the city has to prevent demonstrations from snowballing into the "riots and protests" it experienced in the 1970s.